DESCRIPTION (verbatim from the application): The goal of the proposed research is to use molecular genetic methods to determine the basis for innate immunity in a model organism, Drosophila melanogaster. Upon infection, insects mount an immune response by mobilizing the blood cells and producing a spectrum of antimicrobial peptides to engulf and to lyse the invading microorganisms. This insect self-defense process is similar to the mammalian innate immune system. The innate immune system first recognizes common features of infectious agents, such as the Gram-negative bacteria membrane component lipopolysaccharide (LPS). This leads to signaling events in liver cells, endothelial cells, and macrophages to produce protective molecules and cytokines. These responses serve as the first line defense and help to stimulate B and T lymphocytes of the acquired immune system. Recent studies demonstrate that insect and mammalian innate immunity share a common evolutionary origin. In particular, a Drosophila regulatory factor, Dif, is related to mammalian NF-kappaB. Moreover, the Drosophila transmembrane protein Toll is essential for the activation of Dif, while the mammalian Toll-like receptors activate NF-kappaB and mediate LPS stimulated immune response. Recent results also suggest that Drosophila MAP kinases participate in insect immunity. MAP kinases are mediators of inflammatory response in mammals, further supporting the idea that mammalian and insect immunity employ many homologous molecules. This proposal aims at testing the hypothesis that the Toll signaling, the MAP kinase pathways, and possible novel molecules regulate different aspects of Drosophila immunity. The successful achievement of the proposed research should provide important insights into the evolutionarily conserved immune process in humans. This proposal includes three specific aims: (1) Analyze how Dif protein dimers specifically regulate a subset of immunity genes; (2) Identify novel Dif target genes and new genetic components in the self-defense process; (3) Study the roles of MAP kinase pathways in insect immunity.